1. Field of the Invention (Technical Field)
Embodiments of the present invention relate to the field of compression combustion engines, such as those commonly operated on petrochemical diesel fuel, and more specifically to systems providing the capability to operate such engines on multiple fuels, for example alternative fuels derived from vegetable oils and/or animal fats and/or oils, or combinations of the foregoing.
2. Description of Related Art
Note that the following discussion refers to a publication and that due to a recent publication date, certain publications are not to be considered as prior art vis-à-vis the present invention, discussion of such publication herein is given for more complete background and is not to be construed as an admission that such publication is prior art for patentability determination purposes.
U.S. Patent Publication Number 2008/0163864, to Karner, describes a fuel system for diesel engines which also burn vegetable oil. Karner, however, generates heat to keep the fuel from gelling with electric heaters and does not use the heat generated by the engine, which heat must be dissipated anyway. Karner's system, which has numerous un-heated parts, can operate only with vegetable oil that is liquid at an ambient temperature and cannot operate with alternative oil such as waste grease or hydrogenated or high fat vegetable oils. Karner does mention using engine coolant as an option, but teaches to use the heat from heated engine coolant only to heat the tank.
A diesel engine, sometimes referred to herein as a compression combustion engine to avoid confusion with the petrochemical fuel commonly called diesel, is an internal combustion engine that uses compression ignition, in which fuel ignites as it is injected into air in the combustion chamber that has been compressed to temperatures high enough to cause ignition. Such engines operate using the Diesel cycle named after a German engineer, Rudolf Diesel, who invented it in 1892 based on the hot bulb engine and for which he received a patent on Feb. 23, 1893. Diesel had earlier experimented with the use of coal dust as a fuel in a similar design of engine. At the request of the French Government the Otto company demonstrated the diesel engine at the 1900 Exposition Universelle (World's Fair) using peanut oil. The French government was looking at using peanut oil for a locally produced fuel in their African colonies. Diesel later extensively tested the use of plant oils in his engine and began to actively promote the use of these fuels.
In a typical diesel engine, air is drawn into the cylinders and is compressed by pistons at compression ratios as high as 25:1, much higher than commonly used for spark-ignite engines. Near the end of the compression stroke, fuel is injected into the combustion chamber through an injector (or atomizer). The fuel ignites from contact with the air that, due to compression, has been heated to a temperature of about 700-900° C. (1300-1650° F.). The resulting combustion causes increased heat and expansion in the cylinder which increases pressure and moves the piston downward. A connecting rod transmits this motion to a crankshaft to convert linear motion to rotary motion for use as power in a variety of applications. Intake air to the engine is typically controlled by mechanical valves in the cylinder head.
In cold weather, diesel engines can be difficult to start because the cold metal of the cylinder block and head draw out the heat created in the cylinder during the compression stroke, thus preventing ignition. Some diesel engines use small electric heaters called glow plugs inside the cylinder to help ignite fuel when starting. Some even use resistive grid heaters in the intake manifold to warm the inlet air until the engine reaches operating temperature. Engine block heaters (electric resistive heaters in the engine block) connected to the utility grid are often used when an engine is turned off for extended periods (more than an hour) in cold weather to enable a quicker startup time. Petrochemical diesel fuel is also prone to ‘waxing’ in cold weather, a term for the solidification of diesel oil into a crystalline state. The crystals build up in the fuel (especially in fuel filters), eventually starving the engine of fuel. Low-output electric heaters in fuel tanks and around fuel lines are used to solve this problem. Most modern diesel engines include filter heaters to de-gel diesel fuel. Diesel typically gels at about −20° F., and the aftermarket has supplied heated filters for extremely cold applications for years. Also, most engines have a ‘spill return’ system, by which any excess fuel from the injector pump and injectors is returned to the fuel tank. Once the engine has warmed, returning warm fuel prevents waxing in the tank. This spill return system also cools the diesel fuel when the weather is hot as heat is dissipated through the tank walls by convection. Fuel technology has improved recently so that with special additives, waxing no longer occurs in all but the coldest climates.
Typically, a mechanical injector system vaporizes the fuel. This forced vaporization means that less volatile fuels can be used. More crucially, because only air is inducted into the cylinder in a diesel engine, the compression ratio can be very high as there is no risk of pre-ignition provided the injection process is accurately timed. This means that cylinder temperatures are much higher in a diesel engine than a petrol engine, allowing less combustible fuels to be used. Some large marine diesels (often called cathedral engines due to their size) run on heavy fuel oil (sometimes called “bunker oil”), which is a thick, viscous and almost un-flammable fuel that is very safe to store and cheap to buy in bulk as it is a waste product from the petroleum refining industry. The fuel must be heated to thin it out (often by the exhaust header) and is often passed through multiple injection stages to vaporize it.
Another alternative to petrochemical diesel fuel is vegetable oil. Vegetable oil has any desirable characteristics compared with petrochemical diesel fuel; as examples, it is from renewable sources, it potentially produces less hazardous emissions, and it can be produced by recycling waste products. Effective and convenient operation of diesel engines on vegetable oil, however, has not been achieved due to the many differences between vegetable oil and petrochemical diesel. As an example, vegetable ell solidifies at much higher temperatures than petrochemical diesel, so starting a diesel engine with vegetable oil in even mildly-cold weather is generally impractical. As another example, vegetable oil can leave deposits in fuel lines, cylinders, piston ring, and lube oil that eventually compromises the performance of the engine.
Accordingly, there is a need for systems and methods that allow diesel engines to be operated practically and efficiently on alternative oils such as vegetable oils, animal fats and oils, waste grease, and combinations of the foregoing.